Among substrates on which electronic components are to be mounted, a so-called cavity substrate having electrodes mounted on bottom surfaces of respective apertures (cavities) formed in an upper surface of a substrate body as well as electrodes mounted on the upper surface of the substrate body has hitherto been known. Since the cavity substrate enables three dimensional arrangement of electronic components, the cavity substrate can make up a compact, high-density substrate.
In relation to such a cavity substrate, in order to print the electrodes mounted on the bottom surfaces of the respective cavities (i.e., cavity-area electrodes) and the electrodes mounted on the upper surface of the substrate body (i.e., flat-area electrodes) with paste, like solder, there has been used a screen print system built by coupling a first screen printer to a second screen printer. Specifically, the first screen printer subjects the substrate to screen printing by use of a mask having pattern holes that are provided on downwardly-projecting convex portions to be fitted to the respective cavities and that correspond to the respective cavity-area electrodes. The second screen printer subjects the substrate to screen printing by use of a mask having pattern holes corresponding to the respective flat-area electrodes.
Some of such screen print systems have hitherto been known to have cleaning units provided for the respective screen printers (see; for instance, Patent Document 1). After the substrate has finished undergoing screen printing, the cleaning unit is relatively actuated with respect to a mask in order to prepare for screen printing that is to be performed for a next substrate to be loaded. The cleaning unit brings a mask contact area, which is made by stretching a paper member over an upper end of the cleaning unit, into contact with a lower surface of the mask, to thus clean the paste adhering to the lower surface of the mask.